Database Reference
In-Depth Information
Existing Applications
In many ways, redesigning (or replacing) an existing application can be more
difficult than building a new application to replace a manual process. This is
because there is an existing work flow built around the application, not to
mention the data that has already been stored. Often, the new system will
need to mimic certain behaviors of the existing system while changing the
actual work under the hood. Also, you need to understand the data being
stored and figure out a way to migrate the existing data to the new system.
In addition to formal applications, you should take this time to look for
spreadsheets or end user database solutions, such as Microsoft Access, that
may exist in the organization. Often, data stored on users' computers is just
as important as something that makes it into an enterprise solution. These
“islands of information” exist in the users' domain of control, and typically
this kind of information is hard to pry away from them without manage-
ment intervention.
To analyze and understand the existing application from a data model-
ing standpoint, you should acquire copies of any process flow documents,
data models, data dictionaries, and application documentation (everything
from the original requirements documents to training documents). If noth-
ing else, generate (or ask for) schema definitions for all existing physical
databases, including all tables, views, stored procedures, functions, and so
on. Try to gather screen captures of any application windows that require
user data input, as well as screens that output data to the user. Also, you'll
need the actual code being used by the application as it pertains to data ac-
cess. All these documents will help you understand how the application is
manipulating data; in some cases, there may be specific logic embedded in
the application that can be handled in the database. Knowing this ahead of
time will help prevent confusion during application design.
In addition, you need to look at the application from a functionality
standpoint. Does it do what the customer wants it to do, or are there gaps
in its feature set? This review can be helpful in determining the processes
that you want to carry forward to the new system, processes that should be
dropped, and processes that may be missing from the current system and
need to be added. These existing applications may also provide you with
other system requirements that will be implemented outside the data
model, such as
Access control and security requirements
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Data retention requirements
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Process work flow
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